0001 .. SPDX-License-Identifier: GPL-2.0
0002
0003 .. _kernel_licensing:
0004
0005 Linux kernel licensing rules
0006 ============================
0007
0008 The Linux Kernel is provided under the terms of the GNU General Public
0009 License version 2 only (GPL-2.0), as provided in LICENSES/preferred/GPL-2.0,
0010 with an explicit syscall exception described in
0011 LICENSES/exceptions/Linux-syscall-note, as described in the COPYING file.
0012
0013 This documentation file provides a description of how each source file
0014 should be annotated to make its license clear and unambiguous.
0015 It doesn't replace the Kernel's license.
0016
0017 The license described in the COPYING file applies to the kernel source
0018 as a whole, though individual source files can have a different license
0019 which is required to be compatible with the GPL-2.0::
0020
0021 GPL-1.0+ : GNU General Public License v1.0 or later
0022 GPL-2.0+ : GNU General Public License v2.0 or later
0023 LGPL-2.0 : GNU Library General Public License v2 only
0024 LGPL-2.0+ : GNU Library General Public License v2 or later
0025 LGPL-2.1 : GNU Lesser General Public License v2.1 only
0026 LGPL-2.1+ : GNU Lesser General Public License v2.1 or later
0027
0028 Aside from that, individual files can be provided under a dual license,
0029 e.g. one of the compatible GPL variants and alternatively under a
0030 permissive license like BSD, MIT etc.
0031
0032 The User-space API (UAPI) header files, which describe the interface of
0033 user-space programs to the kernel are a special case. According to the
0034 note in the kernel COPYING file, the syscall interface is a clear boundary,
0035 which does not extend the GPL requirements to any software which uses it to
0036 communicate with the kernel. Because the UAPI headers must be includable
0037 into any source files which create an executable running on the Linux
0038 kernel, the exception must be documented by a special license expression.
0039
0040 The common way of expressing the license of a source file is to add the
0041 matching boilerplate text into the top comment of the file. Due to
0042 formatting, typos etc. these "boilerplates" are hard to validate for
0043 tools which are used in the context of license compliance.
0044
0045 An alternative to boilerplate text is the use of Software Package Data
0046 Exchange (SPDX) license identifiers in each source file. SPDX license
0047 identifiers are machine parsable and precise shorthands for the license
0048 under which the content of the file is contributed. SPDX license
0049 identifiers are managed by the SPDX Workgroup at the Linux Foundation and
0050 have been agreed on by partners throughout the industry, tool vendors, and
0051 legal teams. For further information see https://spdx.org/
0052
0053 The Linux kernel requires the precise SPDX identifier in all source files.
0054 The valid identifiers used in the kernel are explained in the section
0055 `License identifiers`_ and have been retrieved from the official SPDX
0056 license list at https://spdx.org/licenses/ along with the license texts.
0057
0058 License identifier syntax
0059 -------------------------
0060
0061 1. Placement:
0062
0063 The SPDX license identifier in kernel files shall be added at the first
0064 possible line in a file which can contain a comment. For the majority
0065 of files this is the first line, except for scripts which require the
0066 '#!PATH_TO_INTERPRETER' in the first line. For those scripts the SPDX
0067 identifier goes into the second line.
0068
0069 |
0070
0071 2. Style:
0072
0073 The SPDX license identifier is added in form of a comment. The comment
0074 style depends on the file type::
0075
0076 C source: // SPDX-License-Identifier: <SPDX License Expression>
0077 C header: /* SPDX-License-Identifier: <SPDX License Expression> */
0078 ASM: /* SPDX-License-Identifier: <SPDX License Expression> */
0079 scripts: # SPDX-License-Identifier: <SPDX License Expression>
0080 .rst: .. SPDX-License-Identifier: <SPDX License Expression>
0081 .dts{i}: // SPDX-License-Identifier: <SPDX License Expression>
0082
0083 If a specific tool cannot handle the standard comment style, then the
0084 appropriate comment mechanism which the tool accepts shall be used. This
0085 is the reason for having the "/\* \*/" style comment in C header
0086 files. There was build breakage observed with generated .lds files where
0087 'ld' failed to parse the C++ comment. This has been fixed by now, but
0088 there are still older assembler tools which cannot handle C++ style
0089 comments.
0090
0091 |
0092
0093 3. Syntax:
0094
0095 A <SPDX License Expression> is either an SPDX short form license
0096 identifier found on the SPDX License List, or the combination of two
0097 SPDX short form license identifiers separated by "WITH" when a license
0098 exception applies. When multiple licenses apply, an expression consists
0099 of keywords "AND", "OR" separating sub-expressions and surrounded by
0100 "(", ")" .
0101
0102 License identifiers for licenses like [L]GPL with the 'or later' option
0103 are constructed by using a "+" for indicating the 'or later' option.::
0104
0105 // SPDX-License-Identifier: GPL-2.0+
0106 // SPDX-License-Identifier: LGPL-2.1+
0107
0108 WITH should be used when there is a modifier to a license needed.
0109 For example, the linux kernel UAPI files use the expression::
0110
0111 // SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note
0112 // SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note
0113
0114 Other examples using WITH exceptions found in the kernel are::
0115
0116 // SPDX-License-Identifier: GPL-2.0 WITH mif-exception
0117 // SPDX-License-Identifier: GPL-2.0+ WITH GCC-exception-2.0
0118
0119 Exceptions can only be used with particular License identifiers. The
0120 valid License identifiers are listed in the tags of the exception text
0121 file. For details see the point `Exceptions`_ in the chapter `License
0122 identifiers`_.
0123
0124 OR should be used if the file is dual licensed and only one license is
0125 to be selected. For example, some dtsi files are available under dual
0126 licenses::
0127
0128 // SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
0129
0130 Examples from the kernel for license expressions in dual licensed files::
0131
0132 // SPDX-License-Identifier: GPL-2.0 OR MIT
0133 // SPDX-License-Identifier: GPL-2.0 OR BSD-2-Clause
0134 // SPDX-License-Identifier: GPL-2.0 OR Apache-2.0
0135 // SPDX-License-Identifier: GPL-2.0 OR MPL-1.1
0136 // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) OR MIT
0137 // SPDX-License-Identifier: GPL-1.0+ OR BSD-3-Clause OR OpenSSL
0138
0139 AND should be used if the file has multiple licenses whose terms all
0140 apply to use the file. For example, if code is inherited from another
0141 project and permission has been given to put it in the kernel, but the
0142 original license terms need to remain in effect::
0143
0144 // SPDX-License-Identifier: (GPL-2.0 WITH Linux-syscall-note) AND MIT
0145
0146 Another other example where both sets of license terms need to be
0147 adhered to is::
0148
0149 // SPDX-License-Identifier: GPL-1.0+ AND LGPL-2.1+
0150
0151 License identifiers
0152 -------------------
0153
0154 The licenses currently used, as well as the licenses for code added to the
0155 kernel, can be broken down into:
0156
0157 1. _`Preferred licenses`:
0158
0159 Whenever possible these licenses should be used as they are known to be
0160 fully compatible and widely used. These licenses are available from the
0161 directory::
0162
0163 LICENSES/preferred/
0164
0165 in the kernel source tree.
0166
0167 The files in this directory contain the full license text and
0168 `Metatags`_. The file names are identical to the SPDX license
0169 identifier which shall be used for the license in source files.
0170
0171 Examples::
0172
0173 LICENSES/preferred/GPL-2.0
0174
0175 Contains the GPL version 2 license text and the required metatags::
0176
0177 LICENSES/preferred/MIT
0178
0179 Contains the MIT license text and the required metatags
0180
0181 _`Metatags`:
0182
0183 The following meta tags must be available in a license file:
0184
0185 - Valid-License-Identifier:
0186
0187 One or more lines which declare which License Identifiers are valid
0188 inside the project to reference this particular license text. Usually
0189 this is a single valid identifier, but e.g. for licenses with the 'or
0190 later' options two identifiers are valid.
0191
0192 - SPDX-URL:
0193
0194 The URL of the SPDX page which contains additional information related
0195 to the license.
0196
0197 - Usage-Guidance:
0198
0199 Freeform text for usage advice. The text must include correct examples
0200 for the SPDX license identifiers as they should be put into source
0201 files according to the `License identifier syntax`_ guidelines.
0202
0203 - License-Text:
0204
0205 All text after this tag is treated as the original license text
0206
0207 File format examples::
0208
0209 Valid-License-Identifier: GPL-2.0
0210 Valid-License-Identifier: GPL-2.0+
0211 SPDX-URL: https://spdx.org/licenses/GPL-2.0.html
0212 Usage-Guide:
0213 To use this license in source code, put one of the following SPDX
0214 tag/value pairs into a comment according to the placement
0215 guidelines in the licensing rules documentation.
0216 For 'GNU General Public License (GPL) version 2 only' use:
0217 SPDX-License-Identifier: GPL-2.0
0218 For 'GNU General Public License (GPL) version 2 or any later version' use:
0219 SPDX-License-Identifier: GPL-2.0+
0220 License-Text:
0221 Full license text
0222
0223 ::
0224
0225 SPDX-License-Identifier: MIT
0226 SPDX-URL: https://spdx.org/licenses/MIT.html
0227 Usage-Guide:
0228 To use this license in source code, put the following SPDX
0229 tag/value pair into a comment according to the placement
0230 guidelines in the licensing rules documentation.
0231 SPDX-License-Identifier: MIT
0232 License-Text:
0233 Full license text
0234
0235 |
0236
0237 2. Deprecated licenses:
0238
0239 These licenses should only be used for existing code or for importing
0240 code from a different project. These licenses are available from the
0241 directory::
0242
0243 LICENSES/deprecated/
0244
0245 in the kernel source tree.
0246
0247 The files in this directory contain the full license text and
0248 `Metatags`_. The file names are identical to the SPDX license
0249 identifier which shall be used for the license in source files.
0250
0251 Examples::
0252
0253 LICENSES/deprecated/ISC
0254
0255 Contains the Internet Systems Consortium license text and the required
0256 metatags::
0257
0258 LICENSES/deprecated/GPL-1.0
0259
0260 Contains the GPL version 1 license text and the required metatags.
0261
0262 Metatags:
0263
0264 The metatag requirements for 'other' licenses are identical to the
0265 requirements of the `Preferred licenses`_.
0266
0267 File format example::
0268
0269 Valid-License-Identifier: ISC
0270 SPDX-URL: https://spdx.org/licenses/ISC.html
0271 Usage-Guide:
0272 Usage of this license in the kernel for new code is discouraged
0273 and it should solely be used for importing code from an already
0274 existing project.
0275 To use this license in source code, put the following SPDX
0276 tag/value pair into a comment according to the placement
0277 guidelines in the licensing rules documentation.
0278 SPDX-License-Identifier: ISC
0279 License-Text:
0280 Full license text
0281
0282 |
0283
0284 3. Dual Licensing Only
0285
0286 These licenses should only be used to dual license code with another
0287 license in addition to a preferred license. These licenses are available
0288 from the directory::
0289
0290 LICENSES/dual/
0291
0292 in the kernel source tree.
0293
0294 The files in this directory contain the full license text and
0295 `Metatags`_. The file names are identical to the SPDX license
0296 identifier which shall be used for the license in source files.
0297
0298 Examples::
0299
0300 LICENSES/dual/MPL-1.1
0301
0302 Contains the Mozilla Public License version 1.1 license text and the
0303 required metatags::
0304
0305 LICENSES/dual/Apache-2.0
0306
0307 Contains the Apache License version 2.0 license text and the required
0308 metatags.
0309
0310 Metatags:
0311
0312 The metatag requirements for 'other' licenses are identical to the
0313 requirements of the `Preferred licenses`_.
0314
0315 File format example::
0316
0317 Valid-License-Identifier: MPL-1.1
0318 SPDX-URL: https://spdx.org/licenses/MPL-1.1.html
0319 Usage-Guide:
0320 Do NOT use. The MPL-1.1 is not GPL2 compatible. It may only be used for
0321 dual-licensed files where the other license is GPL2 compatible.
0322 If you end up using this it MUST be used together with a GPL2 compatible
0323 license using "OR".
0324 To use the Mozilla Public License version 1.1 put the following SPDX
0325 tag/value pair into a comment according to the placement guidelines in
0326 the licensing rules documentation:
0327 SPDX-License-Identifier: MPL-1.1
0328 License-Text:
0329 Full license text
0330
0331 |
0332
0333 4. _`Exceptions`:
0334
0335 Some licenses can be amended with exceptions which grant certain rights
0336 which the original license does not. These exceptions are available
0337 from the directory::
0338
0339 LICENSES/exceptions/
0340
0341 in the kernel source tree. The files in this directory contain the full
0342 exception text and the required `Exception Metatags`_.
0343
0344 Examples::
0345
0346 LICENSES/exceptions/Linux-syscall-note
0347
0348 Contains the Linux syscall exception as documented in the COPYING
0349 file of the Linux kernel, which is used for UAPI header files.
0350 e.g. /\* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note \*/::
0351
0352 LICENSES/exceptions/GCC-exception-2.0
0353
0354 Contains the GCC 'linking exception' which allows to link any binary
0355 independent of its license against the compiled version of a file marked
0356 with this exception. This is required for creating runnable executables
0357 from source code which is not compatible with the GPL.
0358
0359 _`Exception Metatags`:
0360
0361 The following meta tags must be available in an exception file:
0362
0363 - SPDX-Exception-Identifier:
0364
0365 One exception identifier which can be used with SPDX license
0366 identifiers.
0367
0368 - SPDX-URL:
0369
0370 The URL of the SPDX page which contains additional information related
0371 to the exception.
0372
0373 - SPDX-Licenses:
0374
0375 A comma separated list of SPDX license identifiers for which the
0376 exception can be used.
0377
0378 - Usage-Guidance:
0379
0380 Freeform text for usage advice. The text must be followed by correct
0381 examples for the SPDX license identifiers as they should be put into
0382 source files according to the `License identifier syntax`_ guidelines.
0383
0384 - Exception-Text:
0385
0386 All text after this tag is treated as the original exception text
0387
0388 File format examples::
0389
0390 SPDX-Exception-Identifier: Linux-syscall-note
0391 SPDX-URL: https://spdx.org/licenses/Linux-syscall-note.html
0392 SPDX-Licenses: GPL-2.0, GPL-2.0+, GPL-1.0+, LGPL-2.0, LGPL-2.0+, LGPL-2.1, LGPL-2.1+
0393 Usage-Guidance:
0394 This exception is used together with one of the above SPDX-Licenses
0395 to mark user-space API (uapi) header files so they can be included
0396 into non GPL compliant user-space application code.
0397 To use this exception add it with the keyword WITH to one of the
0398 identifiers in the SPDX-Licenses tag:
0399 SPDX-License-Identifier: <SPDX-License> WITH Linux-syscall-note
0400 Exception-Text:
0401 Full exception text
0402
0403 ::
0404
0405 SPDX-Exception-Identifier: GCC-exception-2.0
0406 SPDX-URL: https://spdx.org/licenses/GCC-exception-2.0.html
0407 SPDX-Licenses: GPL-2.0, GPL-2.0+
0408 Usage-Guidance:
0409 The "GCC Runtime Library exception 2.0" is used together with one
0410 of the above SPDX-Licenses for code imported from the GCC runtime
0411 library.
0412 To use this exception add it with the keyword WITH to one of the
0413 identifiers in the SPDX-Licenses tag:
0414 SPDX-License-Identifier: <SPDX-License> WITH GCC-exception-2.0
0415 Exception-Text:
0416 Full exception text
0417
0418
0419 All SPDX license identifiers and exceptions must have a corresponding file
0420 in the LICENSES subdirectories. This is required to allow tool
0421 verification (e.g. checkpatch.pl) and to have the licenses ready to read
0422 and extract right from the source, which is recommended by various FOSS
0423 organizations, e.g. the `FSFE REUSE initiative <https://reuse.software/>`_.
0424
0425 _`MODULE_LICENSE`
0426 -----------------
0427
0428 Loadable kernel modules also require a MODULE_LICENSE() tag. This tag is
0429 neither a replacement for proper source code license information
0430 (SPDX-License-Identifier) nor in any way relevant for expressing or
0431 determining the exact license under which the source code of the module
0432 is provided.
0433
0434 The sole purpose of this tag is to provide sufficient information
0435 whether the module is free software or proprietary for the kernel
0436 module loader and for user space tools.
0437
0438 The valid license strings for MODULE_LICENSE() are:
0439
0440 ============================= =============================================
0441 "GPL" Module is licensed under GPL version 2. This
0442 does not express any distinction between
0443 GPL-2.0-only or GPL-2.0-or-later. The exact
0444 license information can only be determined
0445 via the license information in the
0446 corresponding source files.
0447
0448 "GPL v2" Same as "GPL". It exists for historic
0449 reasons.
0450
0451 "GPL and additional rights" Historical variant of expressing that the
0452 module source is dual licensed under a
0453 GPL v2 variant and MIT license. Please do
0454 not use in new code.
0455
0456 "Dual MIT/GPL" The correct way of expressing that the
0457 module is dual licensed under a GPL v2
0458 variant or MIT license choice.
0459
0460 "Dual BSD/GPL" The module is dual licensed under a GPL v2
0461 variant or BSD license choice. The exact
0462 variant of the BSD license can only be
0463 determined via the license information
0464 in the corresponding source files.
0465
0466 "Dual MPL/GPL" The module is dual licensed under a GPL v2
0467 variant or Mozilla Public License (MPL)
0468 choice. The exact variant of the MPL
0469 license can only be determined via the
0470 license information in the corresponding
0471 source files.
0472
0473 "Proprietary" The module is under a proprietary license.
0474 This string is solely for proprietary third
0475 party modules and cannot be used for modules
0476 which have their source code in the kernel
0477 tree. Modules tagged that way are tainting
0478 the kernel with the 'P' flag when loaded and
0479 the kernel module loader refuses to link such
0480 modules against symbols which are exported
0481 with EXPORT_SYMBOL_GPL().
0482 ============================= =============================================
0483
0484
0485
